Electroformed screens



` Jan. 20, 1959 G. R., scHAER ELEcTRoFo'RMEn SCREENS Filed Jan. 30, 1956 2 sheets-sheet 1 INVENToR. Glenn R. Scheer ATTORNEYS.

Jam 20, 1959 G. R. scHAER ELECTROFORMED SCREENS 2 Sheets-Sheet 2 Filed Jan. 30, 1956 M 777mm ATTORNEYS;

United States Patent @hice 2,870,068 .Patented Jan. 20, 1,959

ELECTRUFORMED SCREENS Glenn R. Schaar, Columbus, hio, assignor, by mesne assignments, to Diamond Gardner Corporation, a corporation of Delaware Application January 30, 1956, Serial No. 562,151

6 Claims. (Cl. -204-11) This invention relates to `electroformed screens and to Vprocesses forpreparing the same.

Screens have been formed Vpreviously by electrodeposition on a mandrel having metallic portions corresponding to the screen wires and nonconductive portions corresponding to the holes o f the screen. .A difculty with electrodeposition of screens on mandrels of this type to any appreciable thickness is that the holes in the electroformed screen are smallerthan the corresponding nonconductive portions of the mandrel. This is because the electroplate is not confined to the metallic .area of the mandrel but extends over the nonconductive `areas as well, whenever ascreen of appreciable thickness -is electroformed. The` hole size decreases with increasing thickness of the plate, so that the holes become ventirely closed when the screen thickness exceeds the radius of the nonconducting areas of the mandrel. It is impossible to form screens of greater thickness according to prior methods. Thus, the holes of a screen plate on a mandrel having nonconductive areasof .O-.inch diameter substantially are closed when the plate thickness .exceeds .O10 inch, and a screen of greater thickness'thanv .010 inch cannot be formed.

According to the present invention, screens having a high ratio of hole size to wire .size can be electroformed vto desired thickness `sufficient Vfor mechanical strength. To accomplish this, the screens are electroformed on -conductive members which have `holes extending through their entire thickness. The conductive member consti- Atutes the primary cathode in an electroplating bath, which ralso has a secondary cathode. The Vprimary cathode is located between the anode and the .secondary cathode so ,that current flowing from the anode to the secondary cathode must pass through the perforations in the primary cathode. Tlie use of a foraminous primary cathode in conjunction with a secondary cathode in this manner results in electroformed screens in which the hole size can be controlled independently of plate thickness. This makes it possible to produce screens having thicknesses greater than the radii of the nonconducting areas of the mandrel with holes the same size as those in the primary cathode before any metal is plated. The holes in screens formed according yto this invention may be of any desired shape and spacing. Openingsl which are round, square, or any other desired shape may be formed.

The primary cathode is located between the anode and a secondary cathode for electrodeposition according to this invention. The voltage drop between the anode and primary cathode is less than the voltage drop between the anode and secondary cathode. The useful plating current passes from the anode to the primary cathode, and current also passes from the anode to the secondary cathode.

The present invention is susceptible of several embodiments. lt may be used to increase the thickness of thin screens prepared by previously known methods. It may also be used to electroform screens by vnonadherent plating on mandrels. A further use is to prepare mandrels for electroforming the screens of Vthis invention. in whatever embodiment the invention takes, the term mandrel may `be considered to be lthe foraminous primary cathode on which metallic deposition takes place.

Thin vtine-mesh screens ypresently known may be plated to form much thicker screens having appreciable mechanical strength. This is done by'electroplating an adherent metal layer von .a clean metal Ysurface of the original screen. The original screen may be formed in any manner desired, as, for example, by a conventional 4photoengraving process. The screenmay be anygmetal or alloy on which :an adherent electroplated layer can 4be formed, such as nickel, copper, and brass.

vFine-mesh screens may be electroformed according 'to the present invention -by rnonadherent plating on a -mandrel which has a hole and land pattern substantially the same as that desired in the screen. The screen is electroformed on a surface of the mandrel and is then stripped 01T mechanically. The adherence of the screen tothe mandrel is sufcient for it to remain in position during electroforming, and weak enough that it may be :readily removed mechanically.

A perforated mandrel for use in this invention may be prepared by conventional fabricating techniques, ,such as .hole drilling orpunching. It Amay also be prepared lbyiirst forming a screen according to conventional photov.engraving methods, and then electrodepositing the many,drel metal or alloy to desired thickness by the process `of v,this invention.

.The mandrel may be made of any one of various electrically .conductive materials .on which a nonadherent screen plate is normally formed. Such materials are known in the art. Various metals and alloys, such as .stainless steel, lead-coated steel, chromium-plated steel, aluminum, molybdenum, 'and titanium are suitable `as mandrels.

Metals and alloys to which electrodeposited metals Vnormally adhere iirrnly are also suitable for mandrels. Examples of such materials are brass, copper, and nickel. Whenfthe screen metal is one which normally Vadheres Vfirmly to ythe mandrel metal, the mandrel surface is "cov- `eredwith Va 'thin `film r4of -a parting medium to reduce adherence. Such Aparting kmedia are known in the art, and include wax, plastics, resins, asphalt, graphite, and mixtures of these materials.

It is necessary for some materials to provide an insulating coating on the mandrel surface nearest the secondary `cathode to prevent anodic dissolution, since ythe lmandrel is anodic with respect to the secondary cathode. A coating is not necessary in the ycase yof titanium and other materials which are not anodically dissolved.

Any metals and alloys, and laminates thereof, lwhich can be electrop'lated satisfactorily Aby conventional means -to thicknesses equal tothe desired screen thicknesses `may be used as materials for elect-roforming screens according to this invention. Examples of such materials are nickel, copper, brass, and bronze. Screens accordingto the present invention ymaybe made of leither one or more metals.

There is la net current flow from `the anodeI 'to the fcatho'des, `and direct current may be used. In rlieu of direct current, various current cycles which are 4known in the velectroplating art, such as periodic reversal of current, pulsating current, and snper'imposition of alternating current on direct current, may lbeused to obtain smooth electroplates. y

This invention will now be 'described further with reference to the accompanying drawing, in which:

`Fig. l is a iront elevation of oneform or" apparatus according to the present invention;

Fig. "2 is `a top plan view of vthe cathode assembly illustrated 'in Fig. 1;

Fig` 3 is a plan view of a mandrel which forms part of the cathode structure illustrated in Figs. 1 and 2;

Fig. 4 is a front elevational view of a modified form ofthe invention, shown partly in section taken along line 4-4 of Fig. 5, with the front wall of the tank removed; and

Fig. 5 is a sectional view taken along line 5 5 in Fig. 4;

Fig. 6 is a top elevational view, shown partly in section, of a modified cathode assembly for use in the apparatus shown in Figs. 4 and 5;

Fig. 7 is a diagrammatic view of an apparatus for a continuous two-Step electroforming process according to the invention,

Referring now to Figs. l through 3, inclusive, of the drawings, and particularly to Fig. 1, 10 is a tank containing electrolyte 11. In the embodiment shown, tank 10 is an open-top rectangular prism made of glass. Tank 10 may be made of any suitable material which does not react with the electrolyte. For instance, tank 10 may be made of a suitable plastic, or a metal such as steel. With most electrolytes, it is desirable to insulate steel tanks with a lining of rubber, plastic, or the like. Anode 12 is located in tank 1) and is connected to the positive side 13 of a direct-current power supply.

The electroplating apparatus also includes a cathode assembly 14. Cathode assembly 14 includes a container 1S having a bottom 16, side walls 17 and 18 as shown in Fig. 2, and back 19. The top and front of housing 15 are open. Housing 15 is illustrated as being made of a transparent plastic, although it may be made of opaque plastic or other suitable nonconducting material. Located in housing 15 is a foraminous mandrel or screen 20, hav- `ing a screen wire grid which constitutes the primary cathode in the electroplating cell. As shown in Fig. 3, the mandrel preferably has an imperforate border 21. The holes extend through the entire thickness of mandrel 20 so that electrolytes can pass therethrough. In a typical embodiment, the holes have a diameter of about .O10 to .015 inch and are spaced apart about .020 to .025 inch, center to center. As shown in Fig. 3, the holes are arranged in a rectangular pattern. However, the holes in mandrel 20 may be of any desired shape, for example, square, round, or any other desired shape, and may be arranged in any pattern desired. Secondary cathode 22, which is imperforate, is placed inside housing 15 adjacent back wall 19. As shown, secondary cathode 22 is locatedbehind mandrel or screen 20, sothat all current which reaches cathode 22 must pass through the holes in mandrel 20.

Cathodes 20 and 22 are both connected to the negative side of a direct current power supply 23 through its resistances 24 and 25, respectively, which preferably are variable. Ammeters 26 and 27, respectively, may be located in the primary and secondary cathode circuits to indicate the amount of current ilow in each.

The apparatus illustrated in Figs. 1 to 3 is suitable for either building up the thickness of screens by adherent plating or for electroforming screens on mandrels by nonadherent plating. It is particularly suited to the former. When the apparatus is used for building up the thickness of screens, 20 is the the screen to be built up. Screen 20 is cleaned before plating to remove all oxide film and nonconducting materials on the surface. This may be done by known means, such as emery polishing,

is passed from anode 12 to secondary cathode 22 through the holes in screen 29. Nonconductive casing 15 prevents current from reaching secondary cathode 22 by bypassing primary cathode 20 around the edges, as has been pointed out. Preferably the back side of mandrel or screen 20, that is, the side adjacent cathodes 22, is coated with a nonconducting material to prevent dissolution of metal from this surface. The nonconducting material may be an impervious layer of material, such as paint, lacquer, wax, resin, ceramic, or other insulator.

The potentials of cathodes 20 and 22 and the ratio of current to these electrodes is controlled by the amount of resistance in resistors 24 and 25. The potential difference between anode 12 and primary cathode 20 is less than the potential difference between anode 12 and sec` ondary cathode 22. Electroforming according to this invention is most satisfactorily carried out when the potentials of cathodes 20 and 22 are such that the ratio of primary to secondary cathode current is about the same as the ratio of screen-wire area to hole area in screen or mandrel 2t). In other words, the current density on both the lands and holes of mandrel 20 is about the same. When this ratio is maintained, the screen can be plated to substantial thickness with the size of holes and wires substantially the same as that in the original screen. Use of a perforated primary cathode with proper control of primary and secondary cathode currents, as indicated, makes it possible to obtain screens of substantial thickness, with well-defined holes of uniform diameter. Control of the ratio of primary and secondary cathode currents as indicated also results in substantially no deplating of metal from the surface of screen 20 facing secondary cathode 22, even when that screen surface is not coated with nonconductive material.

The hole diameter in the plated portion of screen 20 may be made either larger or smaller than the original screen by proper control of primary and secondary cathode currents. When the ratio of current in the primary and secondary cathode circuits exceeds the ratio of wire area to hole area in screen 20, the holes in the electrodeposited portion of the screen are smaller than those in the original screen, and become entirely closed when the screen is built up to suicient thickness. An advantage of a ratio of primary to secondary cathode current in excess of the ratio of wire area to hole area in screen 20 is that a greater portion of the electrodeposit is formed on the screen 20 and less on secondary cathode 22. When the ratio of primary cathode current to secondary cathode current is less than the ratio of wire area to hole area in screen 20, the holes in the plated portion are larger than the holes on the original screen. Control of the relative amounts of current flowing to cathodes 20 and 22 thus provides a convenient method for controlling the hole size of screens.

While the embodiment of the invention illustrated in Figs. l to 3 has been particularly described with reference to building up screens by adherent electroplating, it is understood that this apparatus is also suitable for electroforming screens on foraminous mandrels by nonadherent electroplating. In that case 20 constitutes the foraminous mandrel on which the screen is electroplated. Mandrel 20 is coated on its entire surface with a nonconductive coating, such as an oxide film. This coating is thin enough on the outer surface so that the ow of current from anode 12 to mandrel 20 is not prevented or even greatly impeded. A screen of substantial thickness having hole diameters the same as the hole diameters in mandrel 20 may be electroformed by maintaining the ratio of current to mandrel 20 to current to secondary cathode 22 about the same as the ratio of wire area to hole area in mandrel 20. The holes in the electroformed screen may be made smaller or larger than those in mandrel 20 by use of larger or smaller ratios of primary to secondary cathode current. After the screen has been electroformed to desired thickness, it is mechanically removed from the mandrel.

Vpass through the holes in foraminous mandrel v44.

asv-sees The potential dilerence between the anode and pri'j mary cathode, primary cathode current density (based on wire area), and other conditions, such as temperature, bath composition, etc., are in the same range as the corresponding conditions in conventional electroplating process using a single cathode. 4 l y y Figs. 4 and 5 illustrate a modified form of the present invention which is particularly kadapted for commercial production of screens. This apparatus makes it possible to electroform screens continuously on a rotating mandrel. In this apparatus, tank is preferably made of metal, s uch as steel, with an insulating lining 31 of rubber or the like. For plating of certain metals, such as copper or tin, a steel tank without any lining may be used. Itis also understood that tank 30 may be made of an insulating material, such as plastic or glass, in which case no lining is necessary. Tank 30 is filled with a bfody of electrolyte 32. Also vshown, are a pair of anode segments 33, each Vsegment of whichis a cylindrical surface of about one-quarter of a cylinder. Anodes 33 are supported in tank 30 by suitable supports 34. Anodes 33 are connected to the positive side of a direct current power supply through conductors 35. Conductors 35 may be of any suitable construction, as for example metallic bars with the ends embedded in cathodes 33. l

Rotatable cathode assembly 4t) includes a shaft 4'1 whichbis journaled for rotation in bearings 42 supported by the side walls of tank 30 and insulated thereform. The details of the bearings 42 are not illustrated, as lthey are 'conventional and lform no part in the present invention. Shaft 41 is preferably hollow, 'as shown. Metallic vdisks 43 are rigidly attached to shaft 41. Primary cathode 44 is fxedly joined to disks 43. Primary cathode 44, which constitutes a mandrel for electroforming screens, is of screenwire construction, having holes which extend therethrough. The primary cathode circuit includes vprimary cathode 44, disks 43, and hollow shaft 41. Suitable -conductors not shown and located exterio'rly of the plating tank 30 connect shaft 41 to a direct current power supply. To protect the metal surfaces of disks 43 from attack by the electrolyte, these surfaces are protected by insulating films 45 and 46, located on the inside and outside surfaces, respectively. As shown in Fig. 5, insulatinglmsr46 include anges 47 which overlie disks 43 and the edges of primary cathodes 44. This construction is desirable to 4prevent excessive plating on the edges 4of screen cathode 44, Awhere otherwise the electroplated layer would `b e thicker than on the greater portion of the srfacefarea of cathode 44. To minimize further the tendency to thicker plating along the edges of screen cathode 44, this cathode is of greater length than anodes 33. By vthese two expedients, the electrodeposit on mandrel 44 Iis of substantially uniform thickness along the entire surface.

Cathode assembly 4t) also includes ahollow cylindrical secondary cathode A48, which is rigidly secured to flanges 43 butbinsulated therefrom by suitable insulating means. All current from the anode which reaches cathode 48 must A conductor 49 passes from secondary cathode 48 through an opening 50 in hollow shaft 4l, and runs on the interior of said hollow shaft 41. Suitable connectors, `not shown, are arranged to connect conductor 49 to the direct current power supply. y The electric current power supply which provides current to'anode 33 and to cathods 44 and 43 may be ofthe :same type as indicated in Fig. l. In other words, anode 33 is connected to the positive side of a direct current power supply, while cathodes 44 and 43 are placed in :series with resistances, not shown, and vconnected'to the ,negative side of a common direct current power'supply.

The apparatus illustrated in Figs. 4 and 5 is particularly :desirable for electroforming screens on a large scale. vThe operation will be described below with'refe'rence toFig. 7. A The'apparatus shown in Figs. 4 and`5 can Yalso'bejused with'slight'modication,"as shownin Fig. 6, for building 6 up the thickness of screensY by the electroforrning process of this invention. All of the apparatus is the same, except for cathode assembly 60, which is of slightly dif ferent construction fromcathode assembly 40 illustrated in Figs; 4 and 5. Cathode assembly 60 has a hollow shaft 61 which may be supported in bearing housings 42, as shown in Figs. 4 and 5. Disks 62, which preferably are made lof plastic or other suitable insulating material, are rigidly secured to shaft 61. Each disk has along its periphery a flange 63 along its outerv face, and a cylindrical land 64 located adjacent to and radially inwardly from ange-63. In operation, anges 63 guide and lands 64 support a screen web which is to be thickened by electr'oplating according to this invention. A hollow metal cylinder 65 which serves as a secondary cathode is rigidly secured to disks 62. Cylinder 65 is electrically connected to shaft 61 by conductor 66.

Fig. 7 illustrates diagrammatically a continuous process fo'r b`o`th electrofor'ming 'a continuous screen web on a mandrel and for Vbuildin'g'up the thickness of said screen web by 'electr'oforming"according to the present invention. The apparatus used isshown in Figs. '4, 5, and 6.

A continuous screen web is electroforrned in lefthand Vtank 30 in Fig. 7. The apparatus in this tank is identical to'that shown in 'detailin Figs. 4 and 5. Cur'- rent flows simultaneously from anodes 33 to mandrel 44, which is the primary cathode, and to secondary cathode 4S. As cathode assembly 40 continuously rotates, an `electrodeposit is formed on mandrel 44. The pattern of holes and lands in the screen corresponds to that 'of mandrel 44. When the desired hole size in the `screen is the same as that in 'mandrel 44, the ratio of primary cathode current to secondary cathode current is about the same as the ratio of land area to hole area on mandrel 44. Smaller yor llarger screen holes are obtained by Vincreasing '.or decreasing, respectively, the ratio ofprim'ary yto secondary cathode current. Control of hole size is thufs effected in the same way as has already been described with reference to Figs. 1 to 3. The electrodepositedsc'reen adheres "suiciently to mandrel 44 to retain its position during electroforming, but weakly enough to permit mechanical removal.

doctor blade not shown.

Screen fweb 7 ti passes through v right-hand electroplati-ng tanktla in-Fig. 7. This tank includes cathode assembly {6} as shown in Fig. 6; otherwise the construction is'as `ventional means located'outsidetank 30m, as for example a'brush connectionformingpart of roller 7l. The ratio of primary to secondary cathode current determines the hole size inthe electroplate as previously described. After screen 70 has been electroplated todesired thicknessin tank 4Stift, it is readyfor further operations, such as cut-' ting into l'desired lengths.

Although both tank 30 and tank 30a are illustrated as the saine size, it is understood that in actual practice they may -be of different sizes, depending upon the thickness of 'the `electrodeposit to be formed in each instance. For instance, if aA screen web is to be electroforrned to an initial thickness of .005 inch in tank 3d, and then plated with van adherent metal layer of .0l0-incl1 thickness in tank ll-so as to'form 'at-etal screen thickness of .015 inch, Vthe cathode 'assembly 66 'and tank 3nd would be approximaetly twice'the size of cathode assembly 40 and tank 30.

y 'lfhe invention'will now be'illustrated by reference to t'rte' folowin'gspecic examples.

As cathode assembly 4t) .rot-ates,jscreen Y70 is separated from mandrel 44 by a secondary cathode.

v'7 Example I A nickel screen which had been electroformed according to the present invention was electroplated with nickel to increase its thickness. A screen 1% by 1% inches was made the primary cathode in an electroplating bath which also had an anode and a secondary cathode. The apparatus used is shown in Figs. 1 to 3. This screen had an initial thickness of 0.0045 to 0.005 inch, except for a slightly greater thickness around the edges, and original hole diameters ranging from .011 to .013 inch with a spacing of 0.020 inch from the center of one hole to the center of the nearest adjacent hole. The surface of this screen was cleaned beforehand to remove all metal oxide and other material and leave a metallic surface. The electroplatng bath had the following composition, pH and temperature:

The cathode current density on the face of the screen, making no allowance for holes, was 100 amperes per square foot. The total current was 1.5 amperes, of which 1.4 amperes flowed to the screen and 0.1 ampere to the Plating was continued for 125 minutes, during which time an adherent electrodeposit nickel layer having a thickness ranging from .007 to .010 inch and holes ranging from .0035 to .005 inch in diameter were plated.

Example 1I Nickel sulfamate, Ni(NH2SO3)2 `.g./l 300 Nickel chloride, NiCl2-6H20 g./l 30 Boric acid, H3BO3 g./l 30 pH 3.1 Temperature F-- 140 The total current passing through the cell was 1.9 am peres, of which 1.42 amperes owed to the screen and the balance to the secondary cathode. The potential difference between the anode and the screen was 3.25 volts, and the potential between the anode and the secondary cathode was 4.6.volts.

Plating was continued for 130 minutes. The electroformed screen weighed 3.413 grams, and the mandrel initially weighed 2.723 grams. The combined weight of screen and mandrel was 6.136 grams. The Weight increase of the secondary cathode was 2.178 grams, from an initial 7.921 grams to a iinal 10.099 grams. This represents 6l percent of the total nickel electrodeposit on the nickel mandrel and 39 percent on the secondary cathode. The thickness of the electrodeposted layer ranged from .010 to .016 inch in addition to the initial thickness of the mandrel. The electroformed layer or screen adhered loosely to the original layer or mandrel, and the two layers could be separated by hand. A thin oxide lm on the surface of the mandrel prevented tight adherence. The holes in the screen had an initial diameter of .Oll to .013 inch and a center-to-center spacing of .023 inch and a final diameter of .009 to .011 inch. The reduction of hole diameter was considerably less than that in Example l. This is attributed to the higher ratio of secondary cathode current to total current in the present example.

While the present invention has been described with reference to flat screens, it is understood that this invention may also be used to electroform and build up shaped screens. Other modifications will be apparent to those skilled in the art. The scope of thepresent invention is limited only by the appended claims.

-What is claimed is:

l. A process for electroforming screens in an electrolytic cell having an anode and primary and secondary cathodes with the primary cathode between the anode and secondary cathode and having a plurality of holes therethrough, comprising non-adherently electroplating a layer of screen material on said primary cathode maintaining the ratio of primary cathode current to secondary cathode current substantially no greater than the ratio of solid area to hole area of the primary cathode, maintaining the potential difference between the anode and the secondary cathode greater than between the anode and the primary cathode, and mechanically removing said layer from said cathode as an entity.

2. A process for electroforming screens in an electrolytic cell having an anode and primary and secondary cathodcs with the primary cathode between the anode and secondary cathode and being a foraminous mandrel having a surface from which electrodeposited metal can be removed, comprising electroplating a layer of screen material on said primary cathode, maintaining the ratio of primary cathode current to secondary cathode current substantially no greater than the ratio of solid area to hole area of the primary cathode, maintaining the potential difference between the anode and the secondary cathode greater than between the anode and the primary cathode, and mechanically removing said layer from said cathode as an entity.

3. A process for electroplating a foraminous mandrel comprising forming an electrolytic cell having therein an anode of one substantially pure metal, a secondary cathode and a primary cathode comprising said mandrel therebetween, simultaneously passing current from said anode to said primary cathode and from said anode to said secondary cathode through said primary cathode maintaining the ratio of primary cathode current to secondary cathode current substantially no greater than the ratio of solid area to hole area of the primary cathode, and maintaining the potential difference between the anode and the secondary cathode greater than between the anode and primary cathode.

4. A process for electroplating a foraminous mandrel comprising forming an electrolytic cell having therein an anode, a secondary cathode, a primary cathode therebetween comprising said mandrel, and an electrolyte comprising at least one metallic salt and being substantially free, of impurities, and simultaneously passing current from said anode to said primary cathode and from said anode to said secondary cathode through said primary cathode maintaining the ratio of primary cathode current to secondary cathode current substantially no greater than the ratio of solid area to hole area of the primary cathode, and maintaining the potential diierence between the anode and the secondary cathode greater than be tween the anode and primary cathode.

5. A process for forming a screen having substantial thickness and undiminished hole size comprising coating a foraminous mandrel with a parting material, form ing an electrolytic cell having therein an anode of one substantially pure metal, a secondary cathode and a primary cathode comprising said mandrel therebetween, simultaneously passing current from said anode to said primary cathode and from said anode to said secondary cathode through said primary cathode maintaining the ratio of primary `cathode current to secondary cathode current substantially no greater than the ratio of solid area to hole area of the primary cathode, maintaining the potential difference between the anode and the secondary cathode greater than between. the anode and primary cathode, removing said mandrel from said cell, and me- 9 chanically stripping the screen formed on said mandrel as an entity from said mandrel.

6. A process for forming a screen having substantial thickness and undiminished hole size comprising coating a foraminous mandrel with a parting material, forming an electrolytic cell having therein an anode, a secondary cathode, a primary cathode therebetween comprising said mandrel, and an electrolyte comprising at least on metallic salt and being substantially free of impurities, simultaneously passing current from said anode to said primary cathode and from said anode to said secondary cathode through said primary cathode, maintaining the -ratio of primary cathode current to secondary cathode current substantially no greater than the ratio of solid area to hole area of the primary cathode, maintaining 15 l@ the potential difference -between the anode and the second ary cathode greater than between the anode and primary cathode, removing said mandrel from said cell, and rnechanically stripping the screen formed on said mandrel 5 as an entity from said mandrel.

References Cited in the file of this patent UNITED STATES PATENTS 1,414,423 Langer May 2, 1922 1,567,791 Duhme Dec. 29, 1925 2,287,122 Norris June 23, 1942 FOREIGN PATENTS 335,161 Great Britain Sept. 15, 1930 

1. A PROCESS FOR ELECTROFORMING SCREENS IN AN ELECTROLYTIC CELL HAVING AN ANODE AND PRIMARY AND SECONDARY CATHODES WITH THE PRIMARY CATHODE BETWEEN THE ANODE AND SECONDARY CATHODE AND HAVING A PLURALITY OF HOLES THERETHROUGH, COMPRISING NON-ADHERENTLY ELECTROPLATING A LAYER OF SCREEN MATERIAL ON SAID PRIMARY CATHODE MAINTAINING THE RATIO OF PRIMARY CATHODE CURRENT TO SECONDARY CATHODE CURRENT SUBSTANTIALLY NO GREATER THAN THE RATIO OF SOLID AREA TO HOLE AREA OF THE PRIMARY CATHODE, MAINTAINING THE POTENTIAL DIFFERENCE BETWEEN THE ANODE AND THE SECONDARY CATHODE GREATER THAN BETWEEN THE ANODE AND THE PRIMARY CATHODE, AND MECHANICALLY REMOVING SAID LAYER FROM SAID CATHODE AS AN ENTITY. 